1. Field of the Invention
The present invention relates to a scanning type display optical system displaying an image by scanning light.
2. Description of the Related Art
A lot of image display apparatuses each apparatus, modulates light by a two-dimensional light modulation device such as a liquid crystal panel, and enlarges and projects the modulated light transmitted through or reflected by the light modulation device on a screen through an optical system, are proposed.
On the other hand, scanning image display apparatuses which displays an image on a screen by scanning a light beam or light beams at high speed, is proposed.
This scanning type image display apparatus can display an image with high color reproducibility in high resolution by using light sources with high directivity such as lasers and selecting appropriate wavelength regions of light beams emitted from the light sources.
Japanese Patent Laid-Open No. 1990-25831, and Japanese Patent Laid-Open No. 1995-168123, propose their specific structure.
In addition, as a scanning type image display apparatus, as proposed in Japanese Patent Laid-Open No. 2001-194617, there is an apparatus that makes an image observable by scanning a light beam in observer""s eyes (his/her retinas).
FIG. 13 shows the structure of the scanning image type display apparatus proposed in the above-described Japanese Patent Laid-Open No. 1995-168123. In this figure, light beams 412, 422, and 432 that have three different wavelength regions and are emitted from rare gas laser sources 410, 420, and 430 are modulated respectively by modulators 414, 424, and 434, and are combined by dichroic mirrors 416, and 426. A combined beam 440 is scanned on a screen 454 in a two-dimensional direction by optical scanning mirrors 444 and 446, and forms a color image on the screen 454.
FIG. 14 shows the structure of an apparatus proposed in the above-described Japanese Patent Laid-Open No. 1990-25831. In this figure, reference numeral 510 shows a Hexe2x80x94Ne laser light source and reference numeral 520 shows an Ar laser light source. A light beam in a red system from the Hexe2x80x94Ne laser source 510 is modulated by an optical modulator 513. In addition, a light beam from the Ar laser light source 520 is split into a green component and a blue component by a beam splitting element 522. And the green and blue components are modulated respectively by different optical modulators 525 and 533.
Thereafter, these three color beams are combined by the dichroic mirrors 528 and 536, and the combined beam enters into a scanning optical system 504. The scanning optical system 504 scans the combined beam two-dimensionally by optical scanning mirrors 542 and 545, and displays a color image on a screen 547.
FIGS. 15(A) and 15(B) show the structure of an optical system that is applied to a head-mounted image display apparatus, proposed in Japanese Patent Laid-Open No. 2001-194617. FIG. 15(A) shows the outline of the optical system, where a light flux from a light source 614 is reflected on a reflecting surface 628 of a prismatic optical system 632 and enters into a scanning mirror 613 after passing through a surface 624 of the prismatic optical system. The scanning mirror 613 scans the incident light. The scanned light enters into the prismatic optical system 632 again, and is reflected on a plurality of surfaces to be emitted from a surface 621 to observer""s pupils 611.
In addition, though the light source 614 is shown like one light source in FIG. 15(A), a dichroic prism 614xe2x80x2 that is a color combining element shown in FIG. 15(B) is actually arranged. Owing to this, three colors of light from light sources 651R, 651G, and 651B corresponding to red, green, and blue are combined by the dichroic prism 614xe2x80x2, and the combined light is emitted toward the prismatic optical system 632.
Nevertheless, since each color combining system in the optical systems proposed in the above-described Japanese Patent Laid-Open No. 1995-168123 and Japanese Patent Laid-Open No. 1990-25831 is formed by combining and arranging a plurality of dichroic mirrors, an optical path route becomes large so that the entire optical system is enlarged. In addition, structure of the color combining system becomes complex since there are a lot of parts.
In addition, though it is possible to miniaturize the optical system, proposed in the above-described Japanese Patent Laid-Open No. 2001-194617, in some measure by using a dichroic prism, in general, the dichroic prism is expensive. Furthermore, since three color light beams are combined by reflective and transmissive actions to a plurality of dichroic surfaces, a shape of the prism becomes complex and it becomes easy to cause displacement of the color light beams on a scan surface.
The present invention aims to provide a scanning type display optical system that can reduce the number of parts and can achieve miniaturization.
In order to achieve the above-described object, the scanning type display optical system according to the present invention includes a plurality of light sources emitting light having wavelength regions mutually different, a light combining element combining the light from the plurality of light sources, and a scanning optical system scanning the light, combined by the light combining element on a scan surface. Then, it is made that the light combining element is a diffraction optical element.
The features of the present invention will become clear by the explanation of the following specific embodiments with referring to drawings.